Science has not proven this, science has proven the exact opposite of this. Make sure you're reading actual science books and not any of this 'New Age' crap about doppelgangers.
My grandmother met my grandfather's doppelgänger. She discovered this AFTER she cold-cocked him, unfortunately. The witnesses were like " Dude that's not ur man, wtf..." She then found out that this doppelgänger was married to HER doppelgänger. Apparently they were nice people.
I'm not saying everyone has one but sometimes you might meet your copy/long-lost twin or some crap. Just don't punch them in the face.
I have an evil doppelgänger living somewhere in the same city as me. I've never seen him but I know he exists because of the things I hear from others and because of the encounters I have with strangers. The police have even mistaken me for him and they are supposed to be trained to spot subtle differences between people.
I'm not saying everyone has one but sometimes you might meet your copy/long-lost twin or some crap. Just don't punch them in the face.